Lun Lun, the 15-year-old Giant Panda, was in labor for about 90 minutes before giving birth to the cubs, her fourth and fifth. The sex of the cubs has not yet been revealed, and the public won't see them until late fall.
The names will be announced when they reach 100 days old, based on a traditional Chinese tradition for good luck.
Zookeepers artificially inseminated Lun Lun back in March with sperm from Yang Yang, the father of all five of Lun Lun's cubs. Until the younger cub arrived at 6:23 p.m., two minutes after its older sibling, the giant panda team had no idea Lun Lun was pregnant with twins.
Twin births do occur in the wild, but typically only one of the cubs will survive because mother will only care for one. In zoos, keepers rotate the cubs with the mother every few hours for the first few months.
Giant pandas are born tiny, and the risk of mortality is very high in the first few months. Twins face even more danger because of their smaller size -- the combined weight of the newborn cubs is just 8.6 ounces.
"This is a success we share with all of our fellow zoological organizations working to understand and protect this iconic species, and we share our joy with our local community and with our colleagues in China,” said Raymond B. King, President and CEO. “Twins are an entirely new scenario for Lun Lun, Zoo Atlanta and our animal care teams, who will no doubt be extremely busy over the next few months.”